Trialkyl amine oxides can be made by reacting a trialkyl amine with aqueous hydrogen peroxide. They are useful for many purposes such as hair conditioners in shampoos as described in U.S. Pat. No. 3,086,943. When a C.sub.10-16 alkyl dimethyl or ethyl alkyl amine oxide as described in U.S. Pat. No. 3,086,943 is made, the product will gel if the concentration of the amine oxide exceeds about 30 weight percent. This results in a fairly dilute aqueous tert-amine oxide solution. When such solutions are shipped to remote locations as they usually are, the freight charges will be fairly high because of the large amount of water that is being shipped.
Alkyl dimethylamine oxides are described in Kirk-Othmer "Encyclopedia of Chemical Technology", 3rd Ed. At page 266, Kirk-Othmer states that "when a strictly aqueous system is employed, final concentrations of amine oxide should be limited to below 35% since higher concentrations tend to gel and prevent good mixing."
Hoh et al., J. Am. Oil Chem. Soc., 40 (1963) page 268-271 describe the synthesis of dimethyl dodecylamine oxide by reaction of dimethyl dodecylamine with 35% aqueous hydrogen peroxide The product is a 30-40 weight percent aqueous solution of the amine oxide. Hoh et al. note that even using 35% aqueous hydrogen peroxide, the reaction mixture will gel unless diluted with water during the reaction
Hoh et al. attempted to make dimethyl dodecylamine oxide without co-feeding water starting with 35%, 70% and 90% aqueous hydrogen peroxide. With 35% and 70% hydrogen peroxide, the product was a gel that could not be stirred. The reaction with 90% hydrogen peroxide was not completed because of darkening of the reaction mixture.
Chadwick U.S. Pat. No. 3,215,741 describes the preparation of di-C.sub.1-2 alkyl C.sub.10-20 alkyl amine oxides by reaction of the tert-amine with hydrogen peroxide While attempting to make the desirable concentrated solutions of the amine oxide, Chadwick found that when commercially available hydrogen peroxide containing 20-90 weight percent H.sub.2 O.sub.2 was used, the reaction sets up to a gel resembling a thick starch paste long before completion of the reaction. Chadwick's solution to the problem was to co-feed at least 20% hydrogen peroxide and sufficient water to the tert-amine such that the final product was water diluted. When dimethyl dodecylamine was used the most concentrated amine oxide solution that could be obtained was only 30-40 weight percent amine oxide.
From the foregoing, it is apparent that a need exists for an amine oxide process that will give a highly concentrated solution of amine oxide without gel formation.